ES2610928T3 - Foam material with very low thermal conductivity and process for its production - Google Patents

Abstract

Thermoplastic foam material, the foam material being a polyester-based material and the polyester consisting of virgin or post-consumer polyethylene terephthalate or a mixture of both, where the foam material is characterized by elongated cells that have a dimensional ratio greater than 1 , 5 and for a density according to ISO 845 of less than 150 kg / m3, preferably less than 80 kg / m3, and for a thermal conductivity of less than 0.032 W / mK measured in accordance with ISO 12677, and which can be obtained by the method of claim 6.

Description

DESCRIPTION

Foam material with very low thermal conductivity and process for its production.

This invention relates to expanded polyester-based materials produced with virgin or post-consumption polyethylene terephthalate characterized by a very low thermal conductivity (<0.032 W / mK). The expanded materials are further characterized in that they are produced by extrusion of a reactive foam 10, improving the intrinsic viscosity (VI) during the extrusion process. The invention encompasses the production of these materials and the use of products made therewith.

Expanded polyester polymers, that is, foam or polyester sponge, are of the greatest importance for a large number of applications, for example 15 related to insulation against temperature gradients, acoustic protection, vibration damping, light construction, etc. Polyester foaming and the use of recycled polyester (post-consumer) are fairly new technologies and it is only possible to find a limited number in the prior art. The concept "foamed polyester" is used in this publication to describe foams where the main component is based on polyester, usually polyethylene terephthalate (PET). It can be mixed with other polymers to improve characteristics, but most (> 60% ) of the mixture is PET The most recent published information on the thermal conductivity of polyester foams can be found in different data sheets of 25 leading manufacturers of polyester foam, such as 3A composites (
http://www.corematerials.3acomposites.com/airex-92.html?&no_cache=

1 & tx_abdownloads_pi1 [action] = getviewclickeddownload & tx_ab downloads_pi1 [uid] = 6), DIAB group (
http://www.diabgroup.com/europe/literature /e_pdf_files/ds_pdf/P_DS_EU.pdf), and Armacell (
http://www.armacell.com/www/ 30 armacell / ACwwwAttach.nsf / ansFiles / ArmaFORM% 20PET_TDS.pdf / $ FILE / ArmaF OR M% 20PET_TDS.pdf). From these tabs it is clear that typical thermal conductivity values are measured in the range of 0.033 to 0.043 W / mK.

EP 0866089 describes that, for physical foaming of polyester,

requires a resin with a significantly higher intrinsic viscosity (VI)

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(VI> 1.2 ml / g) than the standard intrinsic viscosity, especially when lower densities are sought. To achieve the necessary pressure for foaming to occur and prevent cell collapse, high viscosity and high melting resistance are required. Traditionally, a solid state polymerization is used to increase the molecular weight, and therefore the viscosity, to the required level.

Typical polyester foams, similar to other thermoplastic foams such as polyethylene, polypropylene and polystyrene, have a thermal conductivity of the order of 0.032-0.050 W / mK at room temperature.

10 WO 2009/134425 A1 refers to the field of thermal insulation and describes an article comprising a material system with a porosity of at least 95%, said porosity consisting of nanopores comprising incorporated inert gas and having a pore size not exceeding 1,500 nanometers in its shortest dimension. The material can include a polymer, reactive oligomer and / or monomer, the reactive oligomer may comprise an ethylenically unsaturated styrene, urethane and mixtures thereof.

US 4 154 785 A refers to a strong low density thermoplastic resin foam board having solid coating layers and an intermediate layer with large elongated cells, the average size of the cells being able to present in the direction of the thickness of the board a ratio between 1.5 and 5 with respect to the average size of the cells in the longitudinal direction of the board.

US 3 492 249 A describes a (poly) p-phenylene oxide foam having elongated cells, the length of the cells being at least five times larger than their width.

Marcelo Antunes et al. in "Heat Transfer in Polypropylene-Based Foams Produced Using Different Foaming Processes", Advanced Engineering Materials, Vol: 11, No.: 10, Page (s): 811-817, ISSN 1438-1656, describe PP foams with a density less than 150 kg / m3 and a dimensional ratio of up to 9.39.

30 Brief description of the figures

Figure 1: Schematic illustration of the extrusion dies used in the examples, d1 being the distance between the holes and d2 their diameter. Figure 2: Definition of dimensional relationship.

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Figure 3:

Micrograffas of the cellular structure of foams produced in a) comparative example 3 and b) the example of the invention 1.

Figure 4: Schematic presentation of two types of foam: usual PET foam and new PET foam according to the invention.

The invention is described in more detail below in reference to examples.

The invention presented herein describes a thermoplastic foam material according to any one of claims 1 to 5, and a method of producing said foam material according to claim 6, which has a much lower thermal conductivity, by selecting a useful extrusion (matrix with multiple holes) so that the foam material must be stretched significantly, producing a strong cellular orientation with a dimensional ratio greater than 1.5, ideally greater than 2.0. The present invention also describes a foam article obtained from the foam material according to any one of claims 1 to 5. In order for the foam material to withstand said stretching movement, it is also necessary to increase the melt strength by means of a chain extension via a reactive extrusion.

Since high viscosity resins, as described in EP 0866089, cannot be easily achieved, recent technological advances have focused on reactive extrusion. During subsequent foam extrusion it is necessary to add chain extension additives to increase intrinsic viscosity to a level above 1.2 ml / g. For example, EP2163577A1, EP2343330B1, EP2009043B2, EP2048188A1, WO2009149845A1, US4145466A and US5000991 describe these technologies in detail. For this invention a stock mixture (MM) of reactive additives has been used that increases the viscosity by chain extension and branching of side chains during extrusion (described as chain extension concentrate in EP2343330B1). The chemistry of this mother mix is based on the combination of multifunctional chain extender agents for an extension of linear and lateral chains, combined with various antioxidants and process stabilizers incorporated in a carefully selected matrix polymer suitable for PET extrusion. It is also possible to add other additives, for example nucleating agents, fillers, flame retardants, etc., to adjust the

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foam properties. These additives have not been listed in detail because they are considered to be known to specialists. However, less known additives that are not normally used in polyester foam extrusion have also been evaluated, and these could be selected from reflective particles, such as aluminum flakes, graphite powder or metal nanoparticles.

In the invention a twin screw extruder is used. In all the tests described below, a Berstorff® modified double spindle extruder was used. The extruder was equipped with special spindles for PET foaming, with a compression ratio greater than 2.0 and L / D greater than 28. In addition, inverse elements were required to prevent gas leaks back from the injection area. Behind the melting zone, a physical blowing agent or a mixture of physical blowing agents was injected and, consequently, the melt was mixed by means of spindle elements and static mixer. The blowing agents are usually selected from the group consisting of hydrocarbons, fluorocarbons, carbon dioxide, argon, nitrogen or a mixture thereof. In addition, it is also possible to add a chemical blowing agent to improve the efficiency of said blowing agents, or to improve cell structure. In each example, the level of blowing agent (s) was adjusted to obtain the desired density. The resulting mixture of blowing agent and polymer was cooled during extrusion to near the point of crystallization and at the same time a sufficient pressure was maintained controlling the viscosity of the resin and the temperature of the mixture.

The stock mixture (MM) of reactive additives was used at different levels to adjust the viscosity and pressure to a sufficient level (normally at least 60 bar measured in the extrusion head). As the molten gas-laden mixture exited the extruder, the rapid brown pressure caused rapid foaming of the polymer, the size of the cells being controlled by the level of special nucleating agent. The nucleating agent may be an inorganic material (in this case a mother mixture containing talc, organic material or gaseous material). In addition, in those applications where a flame retardant feature is required, a flame retardant additive such as phosphate, halogen, borate, melamine, stannate or a similar component can be used. Then, the foam was cooled and analyzed later in the laboratory. All raw materials were dried to a moisture content of less than 100

ppm before introducing them into the extruder (the resin preferably below 50 ppm).

In this invention, polyester-based materials have been used, preferably virgin and post-consumption polyethylene terephthalate, with an initial VI 5 of 0.56 to 0.82, the polymer VI being increased in one step to a satisfactory level by foam extrusion. reactive and introducing into the mixture at the same time a physical blowing agent. When the mixture leaves the extruder, the VI has reached a level higher than 1.2 ml / g and, consequently, by means of a sudden pressure coffee, the physical blowing agent expands rapidly and foaming occurs. Virgin material is defined as a raw material from a PET producer, which can be supplied in the form of powder or granules (pellets). The post-consumer material is normally available in the form of scales or granules and can contain any type of PET-made products, such as bottles, food packaging material or blisters, which have been collected, crushed and washed by special recycling companies.

The final form of the extrusion product (board) is defined by an extrusion tool (matrix) and in this invention a matrix with multiple holes (US3413387) is used. The diameter of the numerous holes is estimated from the natural expansion factor and, normally, the lower the density, the smaller the holes must be or the greater the distance between the holes (represented as d1 and d2 in the Figure). one). A calibrator is used behind the matrix (called a shaper in WO2005035217), which helps the foam maintain its shape during solidification and cooling. Natural three-dimensional expansion can be promoted by opening the caliper and operating the drive mechanism at the lowest possible speed. This was carried out in one of the examples.

Unexpectedly, it was found that, using the correct reactive extrusion components, the lower density foam can be extruded using an incorrect option of the extrusion tool, that is, with a tool made for a denser product, with a density of 150 kg / m3. If the mixture is defined correctly, the foam will withstand the greatest traction force without breaking. This action produces a foam body with a very elongated cellular structure. This elongated cell structure leads to even more anisotropic properties and, consequently, also to a very low thermal conductivity.

Figure 2 represents the definition of dimensional relationship, which is the length of the cell (see "a" in Figure 2) divided by the height of the cell (see "b" in Figure 2). In circular cells, the value is equal to one (1). The effect of the dimensional relationship on the extruded polystyrene (PE) foams has been studied (Nagata, S. and Koyama, K., "A New Method for Estimating the Cellular Structure of Plastic Foams Based on Dielectric Anisotropy", Pol. Eng. Sci. Vol. 39, No. 5 (1999), pp. 896-903), and the maximum dimensional ratio reached in said study was 1,422, similar to the maximum values measured in the usual PET foams. Most of the values ranged between 0.8 and 1.1.

10 In the examples, three different matrix configurations were used. These are shown in Table 1. The larger diameter tool was designed for higher density products, such as 150 kg / m3, while the smaller diameter tool was designed for low density products, being normally used for densities of 80, 60 and 40 kg / m3.

15 Table 1. Details of extrusion dies used in the examples

 Matrix No. 1 Matrix No. 2 Matrix No. 3

 Distance between holes, d1 (mm)

 6.0 6.0 5.8

 Hole diameter, d2 (mm)

 1.7 1.4 1.1

Comparative Example 1:

An Indorama Ramapet 9921® PET resin was introduced into an extruder together with 2.5% of commercial nucleation agent containing talc and 20.4% of the mother mixture (MM) of reactive additives. The flow rate was maintained

constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 150 kg / m3. The matrix used in this example was No. 1. The calibrator was kept closed and foam expansion was forced. A foam was obtained with cells of a small and uniform size, the cells having an average dimensional ratio of 1.3. No gaps or other lack of homogeneity were observed.

Comparative Example 2:

An Indorama Ramapet 9921® PET resin was introduced into an extruder

together with 2.5% of commercial nucleation agent and with 0.4% of mixture

30 mother (MM) of reactive additives. The flow rate remained constant at 400 kg / h and

the blowing agent was adjusted so that the foamed final product had a

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density of 115 kg / m3. The matrix used in this example was No. 2. The calibrator was kept closed and foam expansion was forced. The foam looked very similar to that of comparative example 1, but it had a slightly larger cell structure and more round cells (less 5 dimensional relationship).

Comparative Example 3:

An Indorama Ramapet 9921® PET resin was introduced into an extruder together with 2.5% commercial nucleating agent and 0.42% stock mixture (MM) of reactive additives. The flow rate was kept constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 80 kg / m3. The matrix used in this example was No. 3. The calibrator was kept closed and foam expansion was forced. A homogeneous foam with a uniform cellular structure was obtained. Figure 3a shows the cell structure.

15 Example of the invention 1:

An Indorama Ramapet 9921® PET resin was introduced into an extruder together with 2.5% commercial nucleating agent and 0.42% stock mixture (MM) of reactive additives. The flow rate was kept constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 80 kg / m3. Matrix No. 3 was now changed to No. 1. The calibrator was kept closed and foam expansion was forced. Due to overexpansion it was necessary to drag the foam at a much higher speed than in comparative example 3. However, a homogeneous and stable foam was obtained, with a clearly elongated cellular structure (see Figure 3). The dimensional ratio increases from an average of 1.4 to more than 2.2, which indicates a significant orientation of the cells.

Comparative Example 4:

An Indorama Ramapet 9921® PET resin was introduced into an extruder together with 2.5% commercial nucleating agent and with 4.0% additive of 30 Kaneka Viscosity booster commercial chain extension extension from Kaneka ®. The flow rate was kept constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 80 kg / m3. The matrix used in this example was No. 1 (similar to the example of the invention

one). The calibrator was kept closed and foam expansion was forced. The

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foam broke inside the calibrator and no foam could be obtained for other tests.

Comparative Example 5:

An Indorama PET resin was introduced into an extruder together with a 2.5% commercial nucleating agent and a 4.0% Kaneka® Viscosity booster commercial chain extension additive from Kaneka®. The flow rate was kept constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 80 kg / m3. The matrix used in this example was No. 1. The calibrator was left open and the foam 10 was allowed to expand freely. A foam with a relatively small extrusion pressure was obtained and the cell structure was thick and heterogeneous.

Example of invention 2:

A post-consumer PET resin granulated from PTP (green PTP-M) was introduced into an extruder together with a 1.25% stock mixture containing 15 aluminum plates (MB Silber 8202 Granule with an aluminum concentration of 40 %) and with 0.52% stock mixture (MM) of reactive additives. 7.5% of a flame retardant, Exolit 950®, was also added to the mixture. The flow rate was kept constant at 400 kg / h and the blowing agent was adjusted so that the foamed final product had a density of 115 kg / m3. The matrix used in this example was No. 1. The calibrator was kept closed and foam expansion was forced. The foam looked very similar to the example of the invention 1, but had more visible gaps, which indicated a higher level of open cells.

Table 2 shows the extrusion conditions of the different examples mentioned above. The higher line speed is due to limited expansion, which should be controlled by excessive drag. In the case of comparative example 4, the viscosity of the material was not sufficiently improved and the foam broke with the drag. Therefore, no extrusion condition could be indicated. Density was measured according to ISO 845.

30 Table 2. Extrusion conditions for different examples

 EC1 EC2 EC3 EI1 EC5 EI2

 Height (mm)

 64.1 65.2 66.7 62.3 59.0 * 61.7

 Width (mm)

 1031 1031 1032 1026 990 * 1024

 Line Speed (m / min)

 1.28 1.32 1.35 1.5 1.21 1.5

 Density (kg / m3)

 148.8 115.6 80.2 79.8 88.6 * 78.9

* Average value: unstable board

All samples obtained from the different examples were analyzed for mechanical properties (in accordance with ISO 844 for compression properties and ISO 1922 for shear properties), water absorption 5 (ASTM C272), steam transmission Water TVA (DIN 52615), average dimensional ratio of cells by microscopy (height and length measurement), and thermal conductivity (according to ISO 12677). Table 3 shows the results.

Table 3. Test results of different examples (- not measured)

 EC1 EC2 EC3 EI1 EC5 EI2

 Compressive strength

 2.35 2.07 0.92 1.01 - 0.99

 (MPa)

 Compression module (MPa)

 58.8 58.4 28.5 32.1 - 30.4

 Shear strength

 1.38 0.96 0.51 0.51 - 0.49

 (MPa)

 Shear Module (MPa)

 32 24 12 14 - 12

 Lengthen shears at break (%)

 14 23 47 42 - 28

 Relac. tell me half cells

 1.3 1.2 1.4 2.2 - 1.9

 Water absorption (%)

 2.8 2.7 3.2 28.8 19.2 45.3

 Lambda at 40 ° C (WmK)

 0.037 0.035 0.034 0.025 0.037 0.024

 TVA

 2210 2100 1945 1560 - 1050

 SBI test (EN13501-1)

 - - Es2d0 Es2d0 - Ds2d0

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The results clearly indicate that the ability of the materials to resist dragging allows a significantly elongated cellular structure, which on the other hand improves thermal conductivity. In addition, a small addition of reflective particles, such as aluminum particles, further improves thermal conductivity. It is recognized that the higher open cell count can also help improve thermal conductivity, but this would not be possible without the drag and the correct choice of the extrusion tool. The two types of foam produced in this study, a standard PET foam and a foam

Highly insulating PET (high dimensional ratio) are schematically represented in Figure 4.

Claims (7)

10 2. fifteen 3. twenty Four. 5. 25 6. Thermoplastic foam material, the foam material being a polyester-based material and the polyester consisting of virgin or post-consumer polyethylene terephthalate or a mixture of both, where the foam material is characterized by elongated cells that have a dimensional ratio greater than 1 , 5 and for a density according to ISO 845 of less than 150 kg / m3, preferably less than 80 kg / m3, and for a thermal conductivity of less than 0.032 W / mK measured in accordance with ISO 12677, and which can be obtained by the method of claim 6. Foam material according to claim 1, characterized in that it has additional polymeric combinations in an amount not exceeding 40% by weight, the additional polymeric combinations being selected from the group consisting of polyethylene terephthalates, polylactic acid, polycarbonate, polyolefins, polyacrylates, polyamides , thermoplastic elastomers, nucleo-shell polymers, liquid crystal polymers (LCP) or mixtures thereof. Foam material according to any of the preceding claims, characterized in that it comprises inorganic reflective additives, such as particles based on aluminum, silver, graphene, carbon nanotubes, clay, mica or graphite. Foam material according to any of the preceding claims, characterized in that it comprises flame retardant additives. Foam material according to any of the preceding claims, characterized in that it is laminated with sheets and / or polymeric layers, wherein the polymers contain glass or carbon and / or aluminum fibers. Manufacturing process for producing the foam material according to any one of claims 1 to 5 by extrusion of reactive foam through a matrix with multiple holes that is selected so that the foam material has to be stretched significantly, producing a strong cellular orientation with a dimensional ratio greater than 1.5, and where the intrinsic viscosity of the polymer increases to 1.2 ml / g or more during reactive extrusion by the addition of chain extension additives and the extruder being equipped with 12 spindles that have a compression ratio greater than 2.0 and an L / D greater than 28, and the extrusion tool being designed for a denser product, with a density of 150 kg / m3 7. Foam article obtained from the foam material according to one of claims 1 to 5.